1. Field of the Invention
The present invention relates to loadbreak connectors and more particularly to improvements in loadbreak connectors which prevent flashover upon switching (opening) the loadbreak connectors.
2. Description of the Prior Art
Loadbreak connectors used in conjunction with 15 and 25 KV switchgear generally include a power cable elbow connector having one end adapted for receiving a power cable and another end adapted for receiving a loadbreak bushing insert. The end adapted for receiving the bushing insert generally includes an elbow cuff for providing an interference fit with a molded flange on the bushing insert. This interference fit between the elbow cuff and the bushing insert provides a moisture and dust seal therebetween.
The elbow cuff forms a cavity having a volume of air which is expelled upon insertion of the bushing insert. During initial movement of the loadbreak connectors in the disassembly operation, the volume of air in the elbow cavity increases but is sealed off at the elbow cuff resulting in a decrease in pressure within the cavity. The dialectric strength of the air in the cavity decreases with the decrease in air pressure. Although this is a transient condition, it occurs at a critical point in the disassembly operation and can result in dialectric breakdown of the opening interface causing a flashover or arc to ground. The occurrence of flashover is also related to other parameters such as ambient temperature, the time relationship between the physical separation of the connectors and the sinusoidal voltage through the loadbreak connectors.
Another reason for flashover while switching loadbreak connectors, prior to contact separation, is attributed to a decrease in dialectric strength of the air along the interface between the bushing insert and the power cable elbow to ground. As earlier described, a decrease in air pressure is momentarily formed by the sealed cavity between the elbow cuff and the bushing insert flange. The lower pressure in the cavity reduces the dialectric strength of the air along the connection interface possibly resulting in flashover.
Accordingly, it would be advantageous to design a loadbreak connector system including a power cable elbow and a loadbreak bushing insert which reduce or prevent the possibility of a flashover upon switching of the connectors.